1. Field of the Invention
The present invention relates to a technique for sampling an analog signal and converting the sampled analog signal to a digital signal.
2. Description of the Related Art
A lot of modern electronic equipment is configured to perform a data processing through an analog to digital conversion (“AD conversion” hereinafter) of analog signal to digital signal (i.e., digital value) to control itself. The analog signal is a sensor output for instance.
The analog signal is prone to an influence of noise, wherein influence causes AD conversion of an analog signal to be overlapped with noise. This generally prompts to compute a weighted average as shown by FIG. 1 to figure out the digital signals (i.e., sampling values) within a certain time period. The example shown by FIG. 1 is a case where seven samplings are taken in a certain time period. In FIG. 1, the “converted values” show the digital signal values (i.e., sampling values) gained by converting respective analog signals. The “averages” show the averages calculated from the digital signal values gained by the respective times. In computing the weighted averages, integration by adding a predetermined number (i.e., weighting) respectively to the digital signals (i.e., sampling values) gained by AD conversion alleviates an influence of noise.
A conventional AD conversion circuit has been configured to conduct a plurality of samplings within a certain time period at a predetermined time interval which is usually very small because of being one n-th the time period for obtaining one piece of digital signal. This has caused a problem of heavy load on a data processing apparatus such as CPU for processing a digital signal obtained by such a sampling.
Presently, multiple functions and low costs are in demand for electronic products, increasing the need to make a data processing apparatus, for processing a digital signal, perform other processing in addition to the digital signal processing. Therefore, a further reduction of the load for processing a digital signal is considered very important. Also highly important is to maintain a precision of the processing.
A conventional AD conversion circuit dealing with an analog signal overlapped with noise is the one noted in a Japanese patent laid-open application publication No. 7-210319. The conventional AD conversion circuit noted in the aforementioned publication is equipped with a switch having a terminal for receiving an analog signal and another terminal being connected with the ground on the front end of the AD converter so as to switch the switch in response to the result of detecting noise, thereby preventing an analog signal overlapped with noise from being sampled by connecting the AD converter with ground when a noise is detected.
In the conventional AD conversion circuit noted in the Japanese patent laid-open application publication No. 7-210319, however, a data processing apparatus must be disposed for the processing in dealing with a change of sampling object, because switching the switch changes the sampling object, hence further increasing the load for processing the digital signal.